Water soluble energy curable stereo-crosslinkable ionomer compositions

ABSTRACT

A homogenous, aqueous, energy curable, stereo cross linkable ionomer containing coating composition and a method of preparing same.

FIELD OF THE INVENTION

This invention relates to the synthesis and use of water soluble energycurable stereo crosslinkable ionomers used in the manufacture of coatedand printed materials.

BACKGROUND OF THE INVENTION

Ionomers are polymeric compounds carrying electronic charges within thepolymer chain. Ionomers build outstanding properties like hardness andsolvent resistance when two or more such polymeric chains create aladder-type structure by salt formation. The ionic complexation ofidentical (e.g., bridged by a higher-valent counterion) or opposingcharges (e.g., acid/base neutralization of amine-functional withcarboxyl-functional polymeric species) on the polymer chains results inadditional crosslinks, the number per unit volume of which determinesthe mechanical strength of the resulting solid. The more commonly usedionic complexation route typically proceeds through use of a more stablecomplex of the bridging counterion with a volatile material (e.g.ammonia) to allow blending in the liquid state followed by latercrosslinking upon drying to a solid. The acid/base neutralization of twooppositely charged ionomers to create crosslinking, in contrast, islargely impractical due to the impossibility of blending these materialsto generate anything other than an intractable crosslinked solid.

DESCRIPTION OF RELATED ART

The photopolymerization approach to ionomer crosslinking is not novel.U.S. Pat. Nos. 6,281,271 and 6,017,982 disclose the energy curing ofethylenically unsaturated ions to build covalent molecular weightin-situ and to trigger crosslinking via ionic complexation of identicalcharges on two or more ionomer chains, in the presence of water and adivalent metaloxide. U.S. Pat. No. 6,180,040 teaches the formation of anionomer via photopolymerization using energy curable compositions ofionic monomers such as metal acrylic carboxylates copolymerized withpolybutadiene resins. These compounds form ionomers upon polymerizationand are bridged over a metal complex in a second (vulcanization) step.In neither of these examples is the bridging ion an organic polymer,either preexisting or formed by in-situ polymerization. Fundamentally,the ionic complexation routes illustrated in the above references yieldmaterials with regular, repeating crosslink patterns and compact ionicstructures.

Ionomers that crosslink only over ethylenically unsaturated moieties(i.e., do not employ either bridging ions or acid/base combinations ofseparate, oppositely charged ionomers or monomers) are commonly used incoatings and photoresists. These compounds are usually water solublepolymers carrying ethylenically unsaturated groups in or grafted ontothe polymer chain of the single-chain ionomer. Examples of these polymertypes are neutralized acrylics described in U.S. Pat. No. 4,275,142;styrene-maleic anhydride described in U.S. Pat. Nos. 3,825,430 and4,401,793; and polyester, or urethane polymer salts described in U.S.Pat. Nos. 6,207,346 and 5,554,712. Since no use is made of the ionicgroups to create additional crosslinks, cured films made from theseionomers are often structurally weakened by the existence of ioniccharges, as these sites retain moisture, which plasticizes the curedfinal polymer (e.g., they show lower rub resistance to water compared touncharged polymers).

U.S. Pat. Nos. 4,745,138; 5,868,605 and 6,099,415 disclose the use ofchemically similar but non-neutralized resins in energy curingcompositions. However, these patents do not teach the formation ofblends with resins, oligomers, or monomers that could potentiallyneutralize an energy curable resin in a way that might crosslink thepolymer. In addition, the viscosity of these non-neutralized resins istypically high. To bring them to application viscosity they must bediluted with either a large amount of a low viscosity reactive monomeror with a solvent.

SUMMARY OF THE INVENTION

The invention is the formation and use of water soluble energy curableionomers that form a stereo crosslinked network upon curing overethylenically unsaturated and polyionic sites. As a result, energycurable stereo-crosslinkable ionomers are produced that deliver a lowviscosity liquid and create a cured solid film having superiormechanical and solvent resistance properties along with good adhesion todifficult substrates. The materials also resist cracking and flaking,and offer improve gloss and rub resistance, and enhanced coverage whencompared to existing materials used in formulating paints, inks, andcoatings.

DETAILED DESCRIPTION

The present invention shows how in-situ photopolymerization can be usedto generate the opposing charge type of polymer from low-viscosityliquid monomer/oligomer blends that have utility in the manufacture ofcoated and printed materials. The structures formed in the presentinvention are random, largely amorphous, three-dimensional networks ofopposing charge polymers with control over the rigidity of thecrosslink. The invention employs lower molecular weight oligomericresins and water as solvent to reduce viscosity and accelerate cure atzero volatile organic content (VOC). Cure occurs in the presence of thewater, and the dissolved water is allowed to concurrently dry withoutapplication of additional energy to give cured structures that aresurprisingly not sensitive to water. The oligomeric resins areneutralized with ethylenically unsaturated polyamines to formwater-soluble resin salts. In some instances these salts are liquids(low melting solids), but more generally they require a water contentabove 10% to be fluid. In most instances, in order to provide usefulviscosity, the water content will be above 30%.

In water based energy curable compositions, viscosity reducing monomericcompounds, typically employed in energy curable compositions arereplaced with water. There are two fundamentally different technologiesused in this field. One derives from ethylenically unsaturated waterbased emulsions, which are dried before curing. The other is based onpartially soluble energy curable material where the curing reaction iscarried out in solution and does not necessarily include a drying stepbefore cure. The precursors employed in the present invention are watersoluble at least partially water-soluble, a state that is obtained fromthe use of truly water soluble monomers and oligomers in admixture withthe required ionic materials.

Ethylenically Unsaturated Resin

The water soluble ethyleneically unsaturated oligomeric or polymericresin may have acid functional groups (e.g. carboxylic acid groups)which are partially or totally neutralized with a base (e.g., an amine)to form a water soluble resin salt. Alternatively, the resin may havebasic functional groups (e.g. amino groups) which are partially ortotally neutralized with an acid (e.g. a carboxylic acid) to form awater soluble resin salt. A preferred embodiment is a neutralizationproduct, where a water soluble, acrylated, resin salt is formed from anethylenically unsaturated energy curable resin containing acrylicgroups, methacrylic groups or a combination thereof; and carboxylic acidfunctional groups, neutralized by a base. While a more preferred resinsalt product is a neutralization product prepared from an ethylenicallyunsaturated amine and a polyanionic resin. Suitable examples of apolyanionic resin are polyacrylic or styrene-maleic anhydridecopolymers, containing carboxyl groups, and having an acid value of atleast 80 (mg KOH per 100 g polymer). Commercially available examples ofsuch resin are Carboset GA-1167 from BF Goodrich; Joncryl 690 from SCJohnson; and SMA 1000 from ELF Atochem. It is preferred that thepolyanionic resin be partially esterified via a polymer analog reactionto tailor the final properties of the compound and the final product ofcompositions containing the compound (propanol, isopropanol, stearicalcohol, polypropylene glycol) but that such resin have the same acidnumber of 80. A preferred modification uses an ethylenically unsaturatedalcohol to form an ethylenically unsaturated polyanionic resincontaining at least two such functions per molecule. The resin is thenneutralized to a pH of at least 5.5 with an ethylenically unsaturatedamine or a mixture such amine and ammonia or other caustic component. Ifthere is no ethylenically unsaturated content in the polyanionic resin,then the tertiary amine should be ethylenically unsaturated. If thepolyanionic resin is ethylenically unsaturated, then the tertiary aminemay be saturated provided that it contains at least two amine groups permolecule. However, it is most preferred that both components of theresin be ethylenically unsaturated.

A particularly preferred energy curable resin is a styrene/maleicanhydride copolymer partially esterified with a hydroxy alkyl acrylateor methacrylate. The hydroxy alkyl acrylate or methacrylate preferablyof such resin is preferably hydroxy butyl acrylate or methacrylate. Apartially esterified styrene/maleic anhydride copolymer may beneutralized without further modification or it may be further partiallyesterified with an alkanol such as butanol, propanol, ethanol and thelike.

The acidic or carboxylic acid (anhydride) groups of the energy curableresin are partially or totally neutralized to provide a resin having thedesired range of water solubility while retaining complete miscibilitywith other water soluble resins.

The resins used to form the compositions of the present invention whilehaving an acid number of at least 80 have a molecular weight between1,000 and 25,000; and more preferably between 1,000 and 10,000; and mostpreferably between 1,000 and 5,000.

Neutralization Agent

Any basic compound (e.g., alkali metal hydroxides such as calciumhydroxide, potassium, hydroxide and sodium hydroxide, ammonia, amines,etc.) may be used to neutralize the acidic groups of the resin.Preferred are ammonia, amines or combinations thereof. Even morepreferred is amines, while more particularly preferred is anethylenically unsaturated tertiary amine. By employing ethylenicallyunsaturated tertiary amines as the neutralizing agent, the acidic groupson the energy curable resin are totally neutralized to form a watersoluble resin having additional polymerizable ethylenic groups. The useof ethylenically unsaturated tertiary amines as the neutralizing agentfurther allows the acid groups on the resin to be totally neutralizedwhich aids in the formation of the stereo cross-linkable water solubleionomers of the present invention.

The ethylenically unsaturated tertiary amine neutralizing agent of thepresent invention has the formula:

wherein R′ is a short chain hydrocarbon group; R″ is H or a methylgroup; and R′″ is selected from the group consisting of C₁-C₂₀ alkyl,C₁-C₂₀ aralkyl, C₁-C₂₀ alkyl substituted aralkyl and C₁-C₂₀ oxyalkylatedderivatives; and a is 1, 2, or 3.

Preferably the ethylenically unsaturated tertiary amine is a MichaelAddition product of a primary or secondary amine (e.g., an alkyl amine)and two acrylic esters, wherein each of the acrylic esters contains twoor more acrylate or methacrylate groups (e.g., wherein the acrylic esteris an acrylate ester or methacrylate ester of an alkane diol, apolyether diol, a glycol, a glycerol). The primary or secondary aminemay be selected, for example, from ethyl amines, ethanol amines,diethanol amines and hexamethylene imines and combinations thereof. Theacrylic ester may be selected from hexanediol diacrylate, dipropyleneglycol diacrylate (DPGDA), tripropylene glycol diacrylate (TPGDA),trimethylolpropane triacrylate (TMPTA), pentaerythritol triacrylate(PETA) and combinations thereof. Examples of commercially availableacrylic functional amines are Laromer 8996 (available from BASF);Ebecryl 7100 (available from UCB); Suncure 175 (available fromReichhold); and Ebecryl P-104 (available from UCB).

Stereo Cross-Linkable Ionomer

It should be noted that the monomeric/oligomeric nature of the ionomercomponents results in a random distribution of the cationic and anioniccharges within the ionomer network (see FIG. 1). This differs fromexisting preformed polymeric ionomer pairs in which one of the pair ofpolymers contains cationic charges while the other contains anioniccharges (see FIG. 2). In the present invention, stereo cross-linkable isdefined as the ability of the oligomeric ionomers to randomly polymerizein-situ via two different mechanisms. The first mechanism being acovalent free radical photopolymerization of the resin. The secondmechanism being an ionic cross-link between the acidic and basicfunctional groups of the resin in multiple dimensions at the same time,to form a highly crosslinked polymeric network of infinite molecularmass. For example, the ethylenically unsaturated tertiary amineneutralizing agent provides the counter ion for the acidic ethylenicallyunsaturated resin, which allows the ionomer formed, to stereo polymerizeduring photoreaction (via energy curing) and form an additionalcross-linked network over the ethylenically unsaturated groups as wellas over the ionic structure of the resin. Therefore, unlike other waterbased energy curable resin technology, where the resistance propertiesto be imparted by the cured resin composition depend on, and are afunction of, the evaporation of the base (e.g. ammonia), for example,which shifts the acid base equilibrium in the post cure composition,here for example, the ethylenically unsaturated tertiary amineneutralizing base, and neutralized resin form an additional cross-linkednetwork instantly on both sides of the ionomer.

Upon irradiation, either or both of the ions formed from the twooligomeric material formations increase in molecular weight by additionpolymerization. The use of (meth)acrylic functional, carboxylicpolymeric, and tertiary amine oligomeric resins in an energy curingmechanism results in the formation of a crosslinked ionomer with aladder structure via the formation of covalent bonds as well as opposingionic bonds. It is essential that one oligomeric material polymerizesbut it is preferred that they both polymerize. After polymerization, ahighly crosslinked structure is formed showing exceptional propertiesover conventional and “water-compatible” energy curable materialsexisting in the prior art. The use of the present composition in energycurable leads to improved cure, adhesion, hardness, mechanical andsolvent resistance properties.

The water solubility of the polymeric resin salt of the presentinvention makes it especially suitable for water based energy curingprocesses while the organic acid/base crosslinking works against thetendency of ionic polymers to become mechanically weaker upon absorptionof water. The control of the molecular weight between acidic and basicsites on separate oligomers allows for the formation of highlycrosslinked materials which show much less brittle failure than expectedfor crosslinked ionomers.

For the synthesis of the resin salt three processes can be used. Thefirst process starts from a solid carboxylic resin, which will bediluted in tertiary acrylic amine and optionally, water. The secondprocess starts with the polymer analog reaction of alcohols with thestyrene maleic anhydride resin in a solvent. In a solvent strippingstep, the resin will be neutralized and diluted with tertiary acrylicamine. In the third process the solvent of the previous described estermodified resin will be azeotropically distilled with water and partiallyneutralized with ammonia. Afterward the resin is further neutralizedwith acrylated amine at 60° C.

EXAMPLE 1 (COMPARATIVE)

SMA-1000 (40 grams, available from Atofina) solid is slurried into water(50 grams) and neutralized to pH 6.5 with concentrated NH₄OH (availablefrom Fisher Scientific). The resulting solution was 43% in solidscontent and had a 31 Pa·s. viscosity at 10 s-1 at 40° C.

EXAMPLE 2

SMA-1000 (40 grams, available from Atofina) solids is slurried intowater (50 grams) and neutralized to pH 6.5 with di(2-hydroxyethyl)methylamine (15 grams, available from Aldrich) with heating to 60° C. for 12hours. The resulting solution was 50% solids in content and had a 30Pa·s. viscosity at 10 s-1 at 40° C.

EXAMPLE 3

SMA-1000 (35 grams, available from Atofina) solids is slurried intowater (50 grams) and neutralized to pH 4.5 with concentrated NH₄OH (5grams, available from Fisher Scientific) followed by addition ofacrylated amine 16-101 (10 grams, available from Reichhold) and heatingto 60° C. for 4 hours. After cooling, the resulting solution wascorrected to pH 6.5 with additional concentrated ammonia and measured tobe 48% in solids content and had a 48 Pa·s. viscosity at 10 s-1 at 40°C.

EXAMPLE 4 (COMPARATIVE)

As described in U.S. Pat. No. 6,559,222, polymeric resin salt, styrenemaleic anhydride copolymer (165 grams) having an acid number of 480 andan average molecular weight of 1000 were added together under agitationto methyl isobutyl ketone (MIBK, 120 grams). The two materials were thenheated to approximately 95-110 degrees C. over 1 to 2 hours under anitrogen blanket. Next, N,N-dimethylbenzyl amine (0.8 grams) and amonofunctional alcohol (18 grams) such as n-propanol, ethanol oroctadecanol were then added to form a polymeric mixture having an acidnumber between 200 to 210. The nitrogen blanket was then removed and4-methoxyphenol (0.12 grams) and N,N-dimethylbenzylamine (0.36 grams)were added. Over a period of time, for example 60 to 90 minutes, ahydroxy-functional acrylate such as 4-hydroxybutyl acrylate (55.80grams) or 2-hydroxy-ethyl acrylate was then added until the acid numberof the polymeric mixture is between 130 to 140. The polymeric mixturewas then distilled and 4-methoxyphenol (0.12 grams) was added along withammonium hydroxide (27.90 grams) and deionized water (327.8 grams). Themixture was then heated, for example to 99 degrees C. The MIBK and waterwere then removed by distillation. When all of the MIBK had beenremoved, the water is returned to the mixture as a water/ammoniadistillate. This material was prepared as a 37% in solids content inwater and neutralized to pH 6.5 with ammonia yielding 23 Pa·s. viscosityat 10 s-1 at 40° C.

EXAMPLE 5

To the resin salt solution (108 grams) as prepared in Example 4 at pH4.5 (containing 37% resin solids in water prior to the final addition ofneutralizing base described in U.S. Pat. No. 6,559,222) at 60° C. wasadded di(2-hydroxyethyl)methyl amine (10 grams, Aldrich). After cooling,the resulting solution had a pH of 6.5 and was 43% in solids content and20 Pa·s. viscosity at 10 s-1 at 40° C.

EXAMPLE 6

To resin salt solution (100 grams) as prepared in Example 4 at pH 4.5(containing 37% resin solids in water prior to the final addition ofneutralizing base described in U.S. Pat. No. 6,559,222) at 60° C. wasadded acrylated amine 16-101 (15 grams, Reichhold) over four hours. Uponcooling, the resulting solution was corrected to pH 6.5 withconcentrated ammonia and measured to be 48% in solids content and had a37 Pa·s. viscosity at 10 s-1 at 40° C.

EXAMPLE 7 (COMPARATIVE)

Laromer 8765 (20 grams, available from BASF Corporation, Mount Olive,N.J.) was added to the resin salt solution (25 grams) as prepared inExample 1, Irgacure 2959 (1.5 grams, available from Ciba) was then addedto this solution. To complete the solution for coating, water (3 grams)and TegoRad 2200N (0.5 grams available from TegoRad Corporation) wereadded with stirring, and the solution set aside for 12 hours to clearthe entrained air before coating and curing. The viscosity of coatingsolution was 0.35 Pa·s. at 25° C.

EXAMPLE 8

Laromer 8765 (17.5 grams, available from BASF) followed by Irgacure 2959(1.5 grams, available from Ciba) were added with stirring to resin saltsolution in water (27 grams) as prepared in Example 2. water (3.5 grams)and TegoRad 2200N (0.5 grams available from TegoRad Corporation) werethen added with stirring, and the solution set aside for 12 hours toclear the entrained air before coating and curing. The viscosity ofcoating solution was 0.38 Pa·s. at 25° C.

EXAMPLE 9

Laromer 8765 (17.5 grams, BASF) followed by Irgacure 2959 (1.5 grams,available from Ciba) were added with stirring to resin salt solution inwater (30.5 grams) as prepared in Example 3. TegoRad 2200N (0.5 gramsavailable from TegoRad Corporation) was then added with stirring, andthe solution set aside for 12 hours to clear the entrained air beforecoating and curing. The viscosity of coating solution was 0.52 Pa·s. at25° C.

EXAMPLE 10 (COMPARATIVE)

Laromer 8765 (17.5 grams, BASF) followed by Irgacure 2959 (1.5 grams,available from Ciba) were added with stirring to resin salt solution inwater (30.5 grams) as prepared in Example 4. TegoRad 2200N (0.5 grams,available from TegoRad Corporation) was then added with stirring, andthe solution set aside for 12 hours to clear the entrained air beforecoating and curing. The viscosity of the coating solution was 0.23 Pa·s.at 25° C.

EXAMPLE 11

Laromer 8765 (17.5 grams, available from BASF) followed by Irgacure 2959(1.5 grams, available from Ciba) were added with stirring to resin saltsolution in water (30.5 grams) as prepared in Example 5. TegoRad 2200N(0.5 grams, available from TegoRad Corporation) was then added withstirring, and the solution set aside for 12 hours to clear the entrainedair before coating and curing. The viscosity of the coating solution was0.28 Pa·s. at 25° C.

EXAMPLE 12

Laromer 8765 (18.0 grams, available from BASF) followed by Irgacure 2959(1.5 grams, available from Ciba) were added with stirring to resin saltsolution in water (30 grams) as prepared in Example 6. TegoRad 2200N(0.5 grams, available from TegoRad Corporation) was then added withstirring, and the solution set aside for 12 hours to clear the entrainedair before coating and curing. The viscosity of the coating solution was0.25 Pa·s. at 25° C.

EXAMPLE 13

The coating solutions described in Examples 7 to 12 were applied by #3and #5 wire-wound rods to Uncoated Leneta N2A charts (Leneta is aproduct and trademark of The Leneta Company, 15 Whitney Rd, Mahwah,N.J.). Immediately following coating, the wet film was cured by passingunder 650 mJ/cm² of UV light (two medium pressure Hg lamps at 300 W/ineach, 200 fpm on an RPC Industries processor) in air. The resultingcured surfaces were conditioned at 75° F. and 48% Relative Humidity forone day and the following measurements taken. Gloss was measured at60-degree angle using a type DIN Geproft 4501 meter from BYK Gardnerparallel to the coating direction. The rub resistance (an methyl ethylketone (MEK) rub and water rub test) was determined by wetting the curedcoating surface and employing light finger pressure to rub the coatingoff as detected by the exposure of the underlying ink. The number ofcomplete back-and-forth cycles required were recorded. Coating adhesionwas measured by taking a convenient length of 610 tape (available from3M Co., St. Paul, Minn.), laminating the tape to the cured surface underfinger pressure, then lifting the tape from the surface in one rapidmotion at right angle to the coated surface. The adhesion was rated apass when the coating remained completely intact and adhered to thesubstrate following tape peel. The coating weight was determinedgravimetrically by the difference in weight between a 10 cm×10 cm piececut from the coated area and an identical size piece cut from a similararea of uncoated stock. Each measurement reported in Table 1 below isnormalized to the same dry coating weight (4 g/m²). TABLE 1 ExampleGloss MEK Rub Water Rub Adhesion  7 (comparative) 65 6 5 fail 10(comparative) 89 12 18 pass 11 91 12 16 pass 12 95 35 20 pass

Those skilled in the art having the benefit of the teachings of thepresent invention as hereinabove set forth, can effect numerousmodifications thereto. These modifications are to be construed as beingencompassed within the scope of the present invention as set forth inthe appended claims.

1. An aqueous, energy curable, homogenous, composition comprising theneutralization product of (a) an ethylenically unsaturated acidic resincontaining carboxylic acid, acrylic functional groups, methacrylicfunctional groups or a combination thereof, and (b) an ammonia, amine,alkali metal hydroxide or a combination thereof; in (c) water; whereupon curing with an actinic radiation source, a stereo-crosslinkedionomer forms offering the composition an increased cross-linkeddensity.
 2. The composition of claim 1 wherein the, ethylenicallyunsaturated resin is a styrene/maleic anhydride copolymer, partiallyesterified with a hydroxy alkyl acrylate or methacrylate functionalgroup.
 3. The composition of claim 2 wherein the partially esterifiedstyrene/maleic anhydride copolymer is further esterified with an alcoholgroup.
 4. The composition of claim 1 wherein the neutralizing agent isammonia, ethylenically unsaturated amine, or a combination thereof. 5.The composition of claim 4 wherein the neutralizing agent is ammonia,ethylenically unsaturated tertiary amine, or a combination thereof 6.The composition according to claim 1, wherein the ethylenicallyunsaturated resin has an acid number of at least 80 and a weight averagemolecular weight between 1,000 and 50,000.
 7. The composition accordingto claim 6, wherein the ethylenically unsaturated resin has an acidnumber of at least 80 and a weight average molecular weight between1,000 and 25,000.
 8. The composition according to claim 7, wherein theethylenically unsaturated resin has an acid number of at least 80 and aweight average molecular weight between 1,000 and 10,000.
 9. An aqueous,energy curable, homogenous, composition comprising: the neutralizationproduct of (d) an ethylenically unsaturated basic resin containingamine, acrylic functional groups, methacrylic functional groups or acombination thereof and (e) an acid; in (f) water, where upon curingwith an actinic radiation source, a stereo-crosslinked ionomer formsoffering the composition an increased cross-linked density.
 10. Anaqueous, energy curable, homogenous, composition comprising: theneutralization product of (a) an ethylenically unsaturatedstyrene/maleic anhydride copolymer acidic resin, partially esterifiedwith a hydroxy alkyl acrylate, further esterified by an alcohol,containing carboxylic acidic functional groups; and (b) an ammonia,ethylenically unsaturated tertiary amine, or a combination thereof; in(c) water, where upon curing with an actinic radiation source, astereo-crosslinked ionomer forms offering the composition an increasedcross-linked density.
 11. A method for preparing an energy curablecoating comprising employing the composition of claim
 1. 12. A methodfor preparing an energy curable coating comprising employing thecomposition of claim
 9. 13. A method for preparing an energy curablecoating comprising employing the composition of claim
 10. 14. An energycurable coating comprising the composition of claim
 1. 15. An energycurable coating comprising the composition of claim
 9. 16. An energycurable coating comprising the composition of claim 10.